1. Field of the Invention
The present invention relates to pistons for internal combustion engines, pumps, compressors and other applications and particularly to cast or forged pistons having oil passages formed at least in part during molding.
2. Description of the Prior Developments
Pistons for use in internal combustion engines and other applications typically are formed with one or more circumferential grooves for receiving one or more piston rings. The grooves are generally formed by a separate machining operation after the piston has been cast or forged. In the case of the oil ring groove, additional machining is typically needed after the groove is formed in order to form drain holes which allow oil to flow through the piston groove to return to an oil sump.
In some cases, cast or forged pistons are subjected to additional machining in order to reduce the weight of the piston. Recesses or bores are machined in the piston, generally in the floor of the piston to remove material and reduce weight.
Although these prior pistons perform adequately, the additional drilling and boring of the oil drain holes adds to the cost of manufacture.
Accordingly, a need exists for a piston having oil drain holes formed in an oil ring groove in such a manner that supplemental machining such as drilling and boring is obviated.